1. Field of the Invention
The present invention relates generally to fault current limiters having superconducting bypass reactors for simultaneous quenching and, more particularly, to a fault current limiter having a superconducting bypass reactor for simultaneous quenching in which, when quenching occurs in a current limiting module, current is bypassed into a superconducting bypass reactor to generate a magnetic field that is evenly applied to the current limiting module provided in the bypass reactor. This causes simultaneous quenching, thus preventing multiple winding modules in the current limiting module from being damaged when voltage is concentrated in one winding module.
2. Description of the Related Art
As is well known to those skilled in the art, fault current limiters (FCLs) in power systems serve to limit mechanical, thermal and electrical stress applied to busbars, electrical insulators, circuit breakers, etc. when a fault current occurs due to short-circuits. Due to an increase in the number of short-circuits and difficulty in the development of power apparatuses that can respond to this, demand for the development of fault current limiters that are able to control a fault current is increasing. However, the development of a practical fault current limiting technique has been delayed by technical problems and difficulty in commercialization.
However, after a high temperature superconductor was discovered, it was feasible to develop a fault current limiter using the nonlinear voltage-current characteristics of a high temperature superconductor. In 1987, the development of high temperature superconducting fault current limiters using liquid nitrogen as a refrigerant began in earnest.
Since superconducting materials have nonlinear resistance, they can be used in fault current limiting devices. Studies on a superconducting fault current limiter using liquid helium as a refrigerant have been slow due to the excessive expense required for refrigeration. However, with the development of a superconducting material that is able to use liquid nitrogen as a refrigerant, various superconducting fault current limiters have been proposed.
When a short-circuit in a system is detected, a high temperature superconducting fault current limiter creates a high resistance using a quenching characteristic in which it is quickly transformed from the superconductivity phase to the normal conductivity phase, thus be having like a fuse and limiting the fault current. Furthermore, the fault current limiter is characterized in that after the fault current has been reduced, it returns to the superconductivity phase.
There have been various kinds of superconducting fault current limiters proposed having the above-mentioned characteristics, for example, resistance type, inductance type, hybrid type, etc.
The resistance type superconducting fault current limiter is characterized in that the structure thereof is simple and it has advantages over the inductance type fault current limiter with respect to expense and weight. However, there are problems in that a heat spot occurs during a fault current limiting process and it requires complicated superconductor manufacturing technique.
The inductance type fault current limiter also uses a superconductor in the same manner as the resistance type fault current limiter. However, the superconductor governs the detection of a short-circuit and controls a switch, and a coil is used as a reactor unlike the resistance type fault current limiter. Under normal conditions, a current flows through the superconductor and there is no impedance in the coil due to perfect diamagnetism of the superconductor. When a short-circuit occurs, the superconductor is quenched which creates an impedance in the coil, thus limiting the current. With regard to this type, there are advantages in that it can be designed into various shapes. The inductance type fault current limiter also has low heat generation since it has no resistance factor. Additionally it has low thermal shock at an initial stage of the fault current limiting process, and it is easy to manufacture the superconductor compared to the resistance type limiter. However, there are disadvantages in that its size increases due to the reactor, and waveform deformation may occur due to additional reactance.
Recently, an electronic/inductance hybrid fault current limiter has been developed. In the hybrid fault current limiter, a superconducting reactor and a DC power supply are provided in a semiconductor diode (or SCR) bridge to limit current. Under normal conditions, an outside current flows through the diode. If the amount of outside current exceeds that of an inside direct current when a short-circuit occurs, the outside current passes through a coil so that the reactance thereof limits the current. However, this method is disadvantageous in that, when a short-circuit occurs, voltage is concentrated on one or only some of the winding modules, and thus the winding modules may be damaged.